JPH0438512B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for controlling the output of a welding power source in a consumable electrode type arc welding method in which short circuits and arc generation are repeated between a consumable electrode and a base metal. Conventional technology Conventionally, in the consumable electrode type arc welding method in which short circuit and arc generation are repeated between the consumable electrode (hereinafter referred to as welding wire) and the molten pool, or the weld base metal, a DC power source with constant voltage characteristics is used as the welding power source. is often used. The welding current output waveform when such a constant voltage DC power source is used is as shown in FIG. In other words, in a conventional constant voltage DC power supply, from the moment the droplet formed at the tip of the welding wire contacts the molten pool and short-circuits, the welding current output increases as determined by the time constant of the electric circuit of the power supply. rate continues to increase until the arc occurs again. Furthermore, after the welding arc is generated again, the welding current decreases at a rate of decrease determined by the above-mentioned time constant until a short circuit occurs again. By the way, if you photograph the welding arc phenomenon with a high-speed camera and observe the occurrence of spatter, you will find that spatter occurs at the moment when the droplets at the tip of the welding wire transfer to the molten pool and the arc re-occurs. It can be seen that a lot of solution is generated at the moment when the solution grows large at the tip of the welding wire and tries to short-circuit with the molten pool.
In particular, the latter is often observed when the average welding current is high. Therefore, it is considered that the cause of spatter is mainly that droplets or a portion of the droplets formed on the welding wire are blown off by the repulsive force of the arc when the arc is generated. The reason why a large amount of spatter occurs when using a conventional constant voltage DC power supply is that the welding current output of this power supply reaches its highest value at the moment of arc regeneration, as shown in Figure 1, and the repulsive force of the arc increases. It is thought that this reached the maximum level and blew away some of the droplets remaining at the tip of the welding wire, causing spatter. In addition, when the average welding current is high, as shown in Figure 2, even if the welding current reaches its minimum value just before welding, the current value at the time of a short circuit is high enough to blow away the droplets immediately after the short circuit. It can be a great source of energy. As described above, with conventional constant voltage DC power supplies, a large amount of spatter is generated, which leads to a decrease in welding efficiency and a reduction in the efficiency of welding work such as the need to remove adhering spatters. However, there remained problems such as adhesion to the shielding nozzle, which obstructed the flow of shielding gas, and nitrogen from the atmosphere mixed into the weld metal, causing deterioration in the mechanical performance of the welded part. To solve these problems, the present inventors lowered the welding current output at the moment of arc regeneration and before and after the droplet short-circuited with the molten pool, and controlled the repulsion energy of the arc to an extent that the solution was not blown away. A method for reducing the amount of spatter generated has already been proposed. This means that by controlling the welding current output as shown in the waveform shown in Figure 3, the amount of spatter generated can be reduced to about 20 to 40% compared to when using a conventional constant voltage DC power supply. This is what I did. The welding current output waveform shown in Fig. 3 is obtained by setting a delay time T _SS in which no welding current energy is applied immediately after the droplet is short-circuited with the molten pool until the short-circuit state is certain, and once the short-circuit is certain, The welding current during short circuit is adjusted so that the droplets can easily transfer to the molten pool.
I'm trying to stream I _SP . After that, when the transfer of the droplets is almost complete and the arc occurs again, the sign of the occurrence of the arc is detected, and at the moment when the arc occurs, the welding current is reduced as described above, and the arc is stopped. Reduce repulsion energy. In addition, after the arc re-occurs, a high current I _AP is applied to form a droplet at the tip of the welding wire, and after maintaining this high current for a predetermined time T _AP , the current is reduced.
It is controlled so that it is lowered to I _AB . this is,
This is because when the solution comes into contact with the molten pool and attempts to short-circuit, the short-circuit occurs more easily with a lower current, and the solution is prevented from being blown away by the repulsive force of the arc. However, the inventors initially fixed the short circuit current I _SP , high current I _AP , high current period T _AP , and low current I _AB to constant values according to the welding wire feeding speed, and performed constant current control. I was doing it. For this reason, the effect of reducing spatter is significant when welding when the welding wire protrusion length, arc length, etc. are maintained appropriately.
The spatter occurrence rate was reduced to 20-40% compared to when using a conventional constant voltage DC power supply. However, after repeated experiments, we found that the effect of reducing the amount of spatter was reduced due to fluctuations in the welding wire feeding speed, fluctuations in the protrusion length of the welding wire, changes in the shape of the molten pool, etc., which are unavoidable in practice. It has been found that there are cases where it becomes unstable. If the high current period T _AP is controlled at constant current as in the past, if a short circuit occurs between the welding wire and the molten pool during the high current period T _AP , spatters will fly off and the welding wire will penetrate, causing the arc to become unstable. Therefore, it is necessary to apply a high current that would normally not cause a short circuit. As a result, the amount of welding wire melted during the high current period was large, the arc length became long, and the constant current period that followed the high current period also tended to be lengthened. Therefore, a flicker phenomenon occurs due to the brightness and darkness of the arc light between the high current period and the low current period, which causes non-uniform bead appearance. Moreover, if for some reason the welding wire and the molten pool come close to each other during a high current period and attempt to short-circuit, it is impossible to prevent this by constant current control. In particular, such accidents are likely to occur during weaving within the groove, and large spatter particles are likely to fly off at this time because the welding wire has a large amount of melting and the arc length is long. Furthermore, if the extension length, that is, the length of the welding wire protruding from the torch, increases, the amount of wire burnout during high current periods will increase due to the influence of Joule heat, and the number of short circuits will decrease. The average arc length also becomes longer. For example, if the anode voltage that contributes to melting is φ, and the welding wire is at 25℃,
The energy required to make molten steel at 1600℃
11.1Jmm ³ and the resistance value of the welding wire is Rext.
The melting amount MR of the welding wire is MR=T _AP (φI _AP +Rext・I _AP ² )/11.1 [mm ³ ]...
It is expressed as (1). Here, T _AP = 11msec, φ = 4.0V,
I _AP = 300A, the resistance value per unit length of welding wire with a diameter of 1.2mm is 1mΩ/mm, and the wire melting amount MR when the extension length is 10mm and 20mm.
Table 1 shows the data converted into welding wire length.
A comparison is shown below. As is clear from Table 1,
The longer the extension length, the greater the amount of wire melting for the same current, resulting in a longer arc length and fewer short circuits, which is unfavorable in terms of work. Therefore, as a result of further detailed investigation of welding phenomena, the present inventors found that even if external conditions change within a certain range, in order to reduce the amount of spatter and stabilize the arc, it is _necessary to It was found that it is possible to control the current voltage using current-voltage characteristics that are different from conventional ones. Purpose The present invention has been made in view of the above circumstances, and its purpose is to control the rate of decrease or increase of welding current at 10 A/V or more as the _TAP welding voltage increases or decreases during the high current period. By doing so, it is an object of the present invention to provide a method for controlling the output of a welding power source that prevents the occurrence of short circuits during high current periods. Overview: When the welding wire and molten pool are short-circuited, a predetermined short-circuit current is applied; a high-current period is when a high-level current is applied for a predetermined time immediately after the arc occurs; and then a low-level current is applied. In the consumable electrode type arc welding method having a period of high current, the output of the welding power source is controlled by setting the rate of decrease or increase of the welding current as the welding voltage increases or decreases to 10 A/V or more during the high current period. Example An example of the present invention will be described below. In this example, the consumable electrode is fed to the base material through a nozzle at a predetermined feeding speed, and while shielding gas is injected from the nozzle, an arc portion is generated between the consumable electrode and the base material. In the consumable electrode type arc welding method, in which welding is performed by repeatedly shorting and generating an arc between the consumable electrode and the base metal, the output current of the welding power source is controlled.
In the output control of this welding power source, there is a period in which a predetermined short circuit current is applied at the time of a short circuit, a high current period in which a predetermined high current is applied immediately after the arc occurs, and a predetermined low current is applied following this high current period. period. In order to prevent short circuits from occurring during the above-mentioned high current period, the arc length may be maintained at an appropriate constant value by bringing the welding voltage as close to constant voltage characteristics as possible during the high current period. Therefore, during high current periods, the rate of decrease in welding current with increasing welding voltage, or
The output of the welding power source is controlled by setting the increase rate of the welding current as the welding voltage decreases to a predetermined value or more. Table 2 shows the amount of spatter generated and the stability of the arc when welding is performed by varying the rate of change K of the welding current due to the change in welding voltage during the high current period T _AP as shown in Figure 4. Shown below. In this case, the appropriate arc voltage value during the high current period T _AP
V _REF is set, and the welding current I _AP during the high current period is corrected based on equation (2) according to the deviation from the actual arc voltage value V _FB . I _AP = -K (V _FB - V _REF ) + 1 ₀ ...(2) As a result, when the current reduction rate due to voltage increase during the high current period is 10 A/V or more, the amount of spatter generated is small and workability is improved. has been improved, especially the current reduction rate.
Shows particularly excellent workability when the voltage is 63A/V or higher.
Table 2 shows the amount of spatter generated during straight welding without shaking the torch on the base metal flat plate, and during weaving welding within the groove, and the welding conditions were a welding wire feed speed of 5.2 m/〓 , the welding wire diameter is 1.2mm. By controlling the high current period with such current-voltage characteristics, compared to constant current control,
The risk of short circuits during high current periods is greatly reduced. Therefore, the current during high current periods can be kept low, and the amount of welding wire melted is therefore reduced, making it possible to shorten the arc length and reduce the size of the droplets, thereby eliminating large spatter. Occurrence can be prevented. Furthermore, it promotes an increase in the number of short circuits, eliminates the flicker phenomenon, and has the effect of maintaining a constant distance between the molten pool and the tip of the welding wire, thereby preventing undulations of the molten pool and improving the appearance of the bead. is also possible. Table 3 shows that in the control method of the present invention, the number of short circuits increases significantly compared to the conventional method. However, the current reduction rate due to voltage increase during the high current period is K = 100A/V
It is. FIG. 5 shows a schematic configuration of a control device for carrying out the control method of the present invention. Reference numeral 1 denotes a V _FB detection circuit, which detects the arc voltage V _FB between the welding wire 2 and the base metal 3. 4 is a V _REF setting circuit, which sets an appropriate arc voltage V _REF in advance. 5 is a K setting circuit that sets the current change rate K, and the current change rate K is 10A/V.
The above values are set. 6 is an _I0 setting circuit for setting the offset amount _I0 . 7 is an arithmetic circuit that receives the current change rate K from the K setting circuit 5, the offset amount I ₀ from the I ₀ setting circuit 6, the arc voltage setting values V _REF and V _FB from the V _REF setting circuit 4, and the current change rate K from the K setting circuit 5; Input the actual value of the arc voltage V _FB and calculate the above equation (2) to calculate the current I _AP during the high current period, and send a signal to the welding power source 8 to output the calculated I _AP . give. Now, during the high current period T _AP , when the arc voltage increases or decreases, the K setting circuit 5
Current change rate K, I ₀ Offset amount from setting circuit 6 I ₀ V Actual value of arc voltage from _FB detection circuit 1
Using V _FB and the arc voltage setting value V _REF from the V _REF setting circuit 4, the calculation circuit 7 calculates the equation (2), and calculates the current I _AP according to the set current change rate K. , a signal for outputting the calculated current I _AP during the high current period T _AP is given to the welding power source 8, and the welding power source 8 supplies this calculated current I _AP to the welding wire during the high current period T _AP .

【table】

【table】

【table】

[Table] Effects As explained above, in the present invention, during the high current period T _AP , the rate of decrease or increase in the welding current as the welding voltage increases or decreases by 10A/
Since the output of the welding power source is controlled at V or higher, the arc can be stabilized and the amount of spatter generated can be reduced. This improves welding efficiency and makes it easier to remove spatter adhering to the base metal. This makes it possible to greatly reduce the number of welding interruptions to remove spatter adhering to the torch nozzle, which is very industrially beneficial.

[Brief explanation of drawings]

Figure 1 is a waveform diagram showing the welding current output waveform when using a constant voltage DC power supply, Figure 2 is a waveform diagram showing the welding current waveform when the average welding current is high and low, and Figure 3 is a waveform diagram showing the welding current waveform when the average welding current is high and low. FIG. 4 is a waveform diagram showing the welding current waveform of a welding power source to which the invention is applied; FIG. 4 is a graph showing the relationship between welding current and welding current for various rates of change in welding current; FIG. 1 is a block diagram showing a schematic configuration of a control device. FIG. 1...V _FB detection circuit, 2...Welding wire, 3...
...Base material, 4...V _REF setting circuit, 6...Arithmetic circuit,
7... Current switching circuit, 8... Welding power source.

Claims (1)

[Scope of Claims] 1. While feeding the consumable electrode to the base material at a predetermined feeding speed, shielding gas is injected from the nozzle to surround the arc generated between the consumable electrode and the base material. In addition, it is a method for controlling the output of a welding electrode used in a consumable electrode type arc welding method in which welding is performed by repeatedly shorting and generating an arc between the consumable electrode and the base metal, and the method includes a period during which a predetermined short-circuit current is applied at the time of a short-circuit. and a method for controlling the output of a welding power source having a high current period in which a predetermined high current is applied immediately after arc generation, and a period in which a predetermined low current is applied following the high current period, A method for controlling the output of a welding power source, characterized in that the rate of decrease or increase in current as the voltage between an electrode and a base metal increases or decreases is 10 A/V or more.